// This is the fully general way to initialise a matrix.// There are shorter ways to specify initialisation,// but this is always what happens under the covers.// Note how you never specify the array's size in its type declaration.int[][]mat;// for each row, allocate a slot for a pointer to an arraymat = new int [3][];for (int i=0; i<3; i++ ){// allocate an array for each rowmat[i]= new int[5];for (int j=0; j<5; j++ ){mat[i][j]= i*j+100;}}